Keyboard switch circuits are generally used as commander units for many kinds of electronic appliances, e.g., calculators, computors, or other key-operated machines.
In typical conventional keyboard switch circuits, as many comparators as keys are usually required and many connections are necessary for connecting the comparators to rows and columns of the keyboard matrix. As a result, known keyboard circuits have several disadvantages. First, large numbers of logic gates are required. Second, the wiring of the elements is correspondingly more complicated. Third, the known circuits cannot directly obtain the binary coded signals associated with the respective keys.